1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having light weight, thin profile and narrow bezel.
2. Discussion of the Prior Art
A liquid crystal display device (LCD) is advantageous in displaying moving images and has high contrast ratio, and is widely used for TV, monitor or the like. The LCD displays images using optical anisotropy and polarization property of liquid crystal.
The LCD includes a liquid crystal panel having two substrates and a liquid crystal layer therebetween, and alignment direction of liquid crystal is changed by an electric field to make difference of light transmittance.
The LCD requires a light source to display images according to the difference of light transmittance of the liquid crystal panel. A backlight unit having the light source is located below the liquid crystal panel.
A CCFL (cold cathode fluorescent lamp), EEFL (external electroluminescent fluorescent lamp), LED (light emitting diode) or the like is used as the light source of the backlight unit.
Among the light sources, the LED is widely used because it has advantages such as small size, low power consumption and high reliability.
The backlight unit is categorized into a direct type and an edge type with respect to location of light source. The edge type has a structure that at least one light source is located at at least one side of a light guide plate, and the direct type has a structure that a plurality of light sources are located directly below the liquid crystal panel.
The direct type backlight unit has limit of thin profile and is thus used for an LCD when brightness is more important than thickness. The edge type backlight unit can achieve light weight and thin profile and is thus used for an LCD for laptop or the like when thickness is more important.
FIG. 1 is a cross-sectional view illustrating an LCD including an edge type backlight unit according to the prior art.
Referring to FIG. 1, the LCD includes a liquid crystal panel 10, a backlight unit 20, a guide panel 30, a bottom cover 50, and a top cover 40.
The liquid crystal panel 10 is a part playing a key role to display images and includes first and second substrates 12 and 14 attached to each other with a liquid crystal layer therebetween.
A backlight unit 20 is located below the liquid crystal panel 10.
The backlight unit 20 includes an LED assembly 29, which is arranged along a length direction of an edge of at least one side of the guide panel 30 and includes a plurality of LEDs 29a and a PCB (printed circuit board) 29b, a white or silver reflecting sheet 25 placed on the bottom cover 50, a light guide plate 23 on the reflecting sheet 25, and an optical sheet 21 on the light guide plate 23.
The liquid crystal panel 10 and the backlight unit 20 are is surrounded by the frame-shaped guide panel 30 and, in such the state, is coupled with the top cover 40 surrounding edges of a top surface at a top side thereof and the bottom cover 50 covering a bottom surface of the backlight unit 20 at a bottom side thereof, and such the components are unified by means of the guide panel 30.
The reference numbers 19a and 19b indicate polarizing plates attached to the top and bottom surfaces of the liquid crystal panel 10, respectively. LCDs are used in desktop computers, monitors, wall mount TVs as well as portable computers, and research to provide large display area and much reduction of weight and volume as well has actively progressed.
Further, the LCD is required to have not only light weight and thin profile and also large display area and small non-display area i.e., narrow bezel.
Accordingly, the case top 40 is formed as a blade type covering one edge of the liquid crystal panel 10, and the liquid crystal panel 10 is attached to and fixed to the guide panel 30 using a adhesive pad such as a double-sided tape, and thus light weight and thin profile, and narrow bezel as well is achieved.
The liquid crystal panel 10, and in more detail, the polarizing plates 19a and 19b attached to both surfaces of the liquid crystal panel 10 are shrunk and expanded due to material property thereof. However, when this phenomenon occurs, since the liquid crystal panel 10 is attached to and fixed to the guide panel 30 using the adhesive pad, deformation due to shrinkage and expansion causes the liquid crystal panel 10 to be warped, and thus light leakage of the liquid crystal panel 10 occurs.
Therefore, display quality of the LCD is degraded.